This sample page demonstrates the idea of Advanced Content Filter (ACF), a sophisticated tool that takes control over what kind of data is accepted by the editor and what kind of output is produced.
ACF controls every single source of data that comes to the editor. It process both HTML that is inserted manually (i.e. pasted by the user) and programmatically like:
editor.setData( '<p>Hello world!</p>' );
ACF discards invalid, useless HTML tags and attributes so the editor remains "clean" during runtime. ACF behaviour can be configured and adjusted for a particular case to prevent the output HTML (i.e. in CMS systems) from being polluted. This kind of filtering is a first, client-side line of defense against "tag soups", the tool that precisely restricts which tags, attributes and styles are allowed (desired). When properly configured, ACF is an easy and fast way to produce a high-quality, intentionally filtered HTML.
Advanced Content Filter is enabled by default, working in "automatic mode", yet
it provides a set of easy rules that allow adjusting filtering rules
and disabling the entire feature when necessary. The config property
responsible for this feature is config.allowedContent.
By "automatic mode" is meant that loaded plugins decide which kind
of content is enabled and which is not. For example, if the link
plugin is loaded it implies that <a> tag is
automatically allowed. Each plugin is given a set
of predefined ACF rules
that control the editor until
config.allowedContent
is defined manually.
Let's assume our intention is to restrict the editor to accept (produce) paragraphs
only: no attributes, no styles, no other tags.
With ACF
this is very simple. Basically set
config.allowedContent to 'p':
var editor = CKEDITOR.replace( textarea_id, {
allowedContent: 'p'
} );
Now try to play with allowed content:
// Trying to insert disallowed tag and attribute. editor.setData( '<p style="color: red">Hello <em>world</em>!</p>' ); alert( editor.getData() ); // Filtered data is returned. "<p>Hello world!</p>"
What happened? Since config.allowedContent: 'p' is set the editor assumes
that only plain <p> are accepted. Nothing more. This is why
style attribute and <em> tag are gone. The same
filtering would happen if we pasted disallowed HTML into this editor.
This is just a small sample of what ACF can do. To know more, please refer to the sample section below and the official Advanced Content Filter guide.
You may, of course, want CKEditor to avoid filtering of any kind.
To get rid of ACF,
basically set
config.allowedContent to true like this:
CKEDITOR.replace( textarea_id, {
allowedContent: true
} );
Please not that disabling filtering is not recommended as it can result in XSS vulnerabilities. It is recommended to rely on the automatic configuration.
ACF is far more than
I/O control: the entire
UI of the editor is adjusted to what
filters restrict. For example: if <a> tag is
disallowed
by ACF,
then accordingly link command, toolbar button and link dialog
are also disabled. Editor is smart: it knows which features must be
removed from the interface to match filtering rules.
CKEditor can be far more specific. If <a> tag is
allowed by filtering rules to be used but it is restricted
to have only one attribute (href)
config.allowedContent = 'a[!href]', then
"Target" tab of the link dialog is automatically disabled as target
attribute isn't included in ACF rules
for <a>. This behaviour applies to dialog fields, context
menus and toolbar buttons.
There are several editor instances below that present different ACF setups. All of them, except the inline instance, share the same HTML content to visualize how different filtering rules affect the same input data.
This editor is using default configuration ("automatic mode"). It means that
config.allowedContent is defined by loaded plugins.
Each plugin extends filtering rules to make it's own associated content
available for the user.
This editor is using a custom configuration for ACF:
CKEDITOR.replace( 'editor2', {
allowedContent:
'h1 h2 h3 p blockquote strong em;' +
'a[!href];' +
'img(left,right)[!src,alt,width,height];' +
'table tr th td caption;' +
'span{!font-family};' +'
'span{!color};' +
'span(!marker);' +
'del ins'
} );
The following rules may require additional explanation:
h1 h2 h3 p blockquote strong em - These tags
are accepted by the editor. Any tag attributes will be discarded.
a[!href] - href attribute is obligatory
for <a> tag. Tags without this attribute
are disarded. No other attribute will be accepted.
img(left,right)[!src,alt,width,height] - src
attribute is obligatory for <img> tag.
alt, width, height
and class attributes are accepted but
class must be either class="left"
or class="right"
table tr th td caption - These tags
are accepted by the editor. Any tag attributes will be discarded.
span{!font-family}, span{!color},
span(!marker) - <span> tags
will be accepted if either font-family or
color style is set or class="marker"
is present.
del ins - These tags
are accepted by the editor. Any tag attributes will be discarded.
Please note that UI of the
editor is different. It's a response to what happened to the filters.
Since text-align isn't allowed, the align toolbar is gone.
The same thing happened to subscript/superscript, strike, underline
(<u>, <sub>, <sup>
are disallowed by
config.allowedContent) and many other buttons.
This editor is using a custom configuration for ACF. Note that filters can be configured as an object literal as an alternative to a string-based definition.
CKEDITOR.replace( 'editor3', {
allowedContent: {
'b i ul ol big small': true,
'h1 h2 h3 p blockquote li': {
styles: 'text-align'
},
a: { attributes: '!href,target' },
img: {
attributes: '!src,alt',
styles: 'width,height',
classes: 'left,right'
}
}
} );
This editor is using a custom set of plugins and buttons.
CKEDITOR.replace( 'editor4', {
removePlugins: 'bidi,font,forms,horizontalrule,iframe,justify,table,tabletools,smiley',
removeButtons: 'Anchor,Underline,Strike,Subscript,Superscript,Image',
format_tags: 'p;h1;h2;h3;pre;address'
} );
As you can see, removing plugins and buttons implies filtering.
Several tags are not allowed in the editor because there's no
plugin/button that is responsible for creating and editing this
kind of content (for example: the image is missing because
of removeButtons: 'Image'). The conclusion is that
ACF works "backwards"
as well: modifying UI
elements is changing allowed content rules.
This editor is built on editable <h1> element.
ACF takes care of
what can be included in <h1>. Note that there
are no block styles in Styles combo. Also why lists, indentation,
blockquote, div, form and other buttons are missing.
ACF makes sure that
no disallowed tags will come to <h1> so the final
markup is valid. If the user tried to paste some invalid HTML
into this editor (let's say a list), it would be automatically
converted into plain text.
This editor is using a custom configuration for ACF.
It's using the
Disallowed Content property of the filter to eliminate all title attributes.
CKEDITOR.replace( 'editor6', {
allowedContent: {
'b i ul ol big small': true,
'h1 h2 h3 p blockquote li': {
styles: 'text-align'
},
a: {attributes: '!href,target'},
img: {
attributes: '!src,alt',
styles: 'width,height',
classes: 'left,right'
}
},
disallowedContent: '*{title*}'
} );